Also run the build workflow on PRs to a release branch

Author: sandhose

.github/workflows/build.yaml

@@ -10,7 +10,9 @@ on:
 
   # Only run for pull requests if relevant files were changed
   pull_request:
-    branches: [main]
+    branches:
+      - main
+      - 'release/**'
     paths:
       - Dockerfile
       - docker-bake.hcl